The metal-oxide-semiconductor (MOS) transistor is one type of field effect transistor (FET). The MOS transistor typically includes a source, a drain region, a gate oxide layer, and a gate formed on a semiconductor substrate.
According to a conventional method of manufacturing a MOS transistor device, a gate oxide layer is formed on a device active region of a semiconductor substrate. Next, a polycrystalline silicon layer is formed on the gate oxide layer and a photoresist layer is deposited on the polycrystalline silicon layer. The photoresist layer is then exposed and developed to form a photoresist layer pattern that exposes and covers predetermined areas of the polycrystalline silicon layer.
Subsequently, using a process such as end point detection (EDP), the photoresist layer pattern is used as a mask to etch the exposed areas of the polycrystalline silicon layer. As a result, a predetermined width of the polycrystalline silicon layer that remains forms a gate of the MOS transistor device.
However, during the exposing and developing of the photoresist layer, because light is reflected from the polycrystalline silicon layer formed thereunder, it is difficult to form a pattern to precise and desired dimensions. This problem becomes more severe as higher levels of integration are pursued, that is, as pattern dimensions decrease in size.
With continuous increases in the level of device integration, it is becoming more and more difficult to realize a MOS transistor gate having a small width. To overcome this difficulty, an organic or inorganic anti-reflection coating (ARC) is formed on the polycrystalline silicon layer. However, even with the use of an ARC, limits with regard to the patterning dimensions of the photoresist layer remain. In particular, using present patterning processes, a gate having a width of 0.18 μm may be formed, but it becomes difficult to form a gate having a smaller width of, for example, 0.15 μm or 0.13 μm, 0.09 μm, etc.
Conventional techniques related to forming a gate of a small width are disclosed in U.S. Pat. Nos. 6,583,009; 6,569,736; 5,479,368; and 6,358,827.